1. Field of the Invention
The present invention relates generally to devices and methods for making temperature measurements. More particularly, the present invention relates to devices and methods for measuring the temperature of a semiconductor substrate through non-contact arrangements utilizing a temperature sensitive member located adjacent the substrate to be measured.
2. Background of the Art
The fabrication of semiconductor devices on substrates typically requires the deposition and etching of multiple metal, dielectric and other semiconductor film layers on the surface of a substrate. The film layers are typically deposited onto, and etched from, the substrates in vacuum chambers. Controlling the deposition and etch rate uniformity are critically important to the manufacture of integrated circuits. One of the parameters which must be tightly controlled during such deposition or etching process is the film temperature, which is particularly important for fabricating semiconductor multilayer structures from silicon (Si) or gallium arsenide (GaAs). It is also critical to obtaining high-T.sub.c (high critical temperature) superconductor film of optimal quality on a substrate.
There are many methods currently used for temperature measurement of the substrate or film layer. One common technique is to locate thermocouples thermistors or resistance thermometers in the chamber to inferentially measure the substrate temperature. In some cases, the temperature measuring device has been embedded in the substrate support where it is protected from the environment of the vacuum chamber. An electrical signal is generated by the device, which is then converted into temperature readings or employed for control functions.
In certain situations, it is necessary or desirable to obtain temperature data by non-electrical techniques. This may occur: (1) where temperatures over large areas are to be measured and measurement by a dense distribution of thermocouples thus becomes impractical; (2) where the attachment of thermocouples and leads to the chamber would alter the temperatures to be measured; (3) in environments where, because of high electric or magnetic fields, metallic wires are undesirable; (4) where electrical isolation and/or insensitivity to electrical noise generation is desired; (5) where, because of motion or remoteness of the part to be sensed, permanent lead wires are impractical; or (6) where, because of corrosive chemical environments, wires and thermocouple junctions would be adversely affected, with resultant changes in electrical characteristics and erratic or erroneous temperature readings. For example, a plasma, such as used in chemical vapor deposition, can have an adverse effect on conventional temperature monitoring probes placed in physical contact with the substrate, and any contact between the probe and the substrate may cause substrate defects in the vicinity of the contact area. Such contact can cause high-density circuitry formed on the substrate near the contact area to be destroyed, thereby reducing substrate yield and the number of chips recoverable from a single substrate.
The above considerations are important for determining production worthiness of processing tools used for adding and removing materials from semiconductor substrates. A dielectric substrate formed of silicon or a III-V or II-IV compound, such as gallium arsenide or zinc telluride, is typically processed in a high-vacuum environment. This environment can have an adverse effect on conventional temperature monitoring probes placed in physical contact with the substrate, and contact between the probe and the substrate may cause substrate defects in the vicinity of the contact area. Such contact can cause high-density circuitry formed on the substrate near the contact area to be destroyed, thereby reducing substrate yield and the number of chips recoverable from a single substrate.
Therefore, in some process situations, radiation pyrometry techniques are preferable since they measure the temperature of an object by means of the quantity and character of the energy which it radiates. These techniques can be applied to semiconductor manufacturing to avoid the problems associated with temperature probes being in contact with the substrate. Therefore, optical pyrometers and light probes may be used to monitor substrate temperature by comparing the in-spectral intensity of the hot substrate with that of a source of standard intensity. To provide an accurate indication of substrate temperature from an optical pyrometer, the emissivity of the substrate must be known. With currently available pyrometer techniques, it is very difficult, if not impossible, to ascertain accurately emissivity of a semiconductor substrate undergoing processing for manufacture of integrated circuits. At temperatures below approximately 600.degree. C., undoped silicon is transparent to infrared energy. As the temperature or doping level of the substrate increases, the substrate becomes less transparent to infrared energy. The decrease in transparency causes the emissivity of radiant energy that can be detected by an optical pyrometer to change in a fairly unpredictable manner. Emissivity of optical energy from the substrate is also dependent on how rough the substrate emitting surface is. In addition, substrate emissivity as a whole is a function of material deposited on the face of the substrate in the optical pyrometer field of view. Since emissivity from the substrate is variable, the output of the optical pyrometer is frequently not an accurate indication of substrate temperature.
Presently, the optical techniques used to measure temperature of a substrate require placement of a temperature sensitive material onto the backside of a substrate so that the decay of that material and light emissions associated therewith can be measured. A light probe is housed within the support member below the substrate receiving surface of the support member. The light probe excites the temperature sensitive material and causes it to emit radiation. The emitted radiation is quantified and compared with known temperature values. One drawback to this method is that it requires additional processing steps to be performed on the substrate prior to the continual formation of integrated circuits thereon. In addition to increased cost and time, the material deposited on the substrate for this purpose may jeopardize the integrated circuits ultimately formed on the substrate.
U.S. Pat. No. 4,560,286, entitled "Optical Temperature Measurement Techniques Utilizing Phosphors", Wickersheim, incorporated herein by reference, describes a method and apparatus for measuring the temperature of an object provided with a phosphor material layer that emits at least two optically isolatable wavelength ranges whose intensity ratio depends upon the object or environment temperature. The emitted radiation is quantified by an optical system that may include an optical fiber. One known application utilizing this art is the measurement of substrate temperature by providing a small amount of temperature sensitive material on the backside of the substrate. A light detecting member is provided within the substrate support member normal to the surface on which the temperature sensitive material is placed to measure the emitted radiation from the temperature sensitive material. A processor quantifies the emitted radiation and determines the temperature of the substrate.
This technique, however, requires that the temperature sensitive material be placed on the backside of the semiconductor substrate. This poses several problems. First, the phosphor material may migrate into the silicon substrate on which it is provided. Second, the process of applying the temperature sensitive material to the backside of the substrate requires additional processing steps which are both time consuming and expensive.
Therefore, there exists a need for an apparatus and method for determining the temperature of a substrate during processing through a non-contact arrangement utilizing optical techniques which eliminate the need to deposit temperature sensitive material on the substrate.